Rotary kiln control apparatus and programming

ABSTRACT

Rotary kiln operation is controlled so as to result in satisfactory kiln performance and high quality clinker production over long periods of time. Main burner fuel supply is controlled when the maximum temperature of materials in the kiln is in one range, and kiln speed of rotation is controlled when such maximum temperature is in another range. Also, air is passed to the kiln via a clinker cooler, for preheating, and the cooler speed of movement is controlled in relation to kiln speed of rotation and raw mix feeder speed.

klni ted States Patent Inventor Joseph H. Herz [56] References Cited Y r L n 111W- UNITED STATES PATENTS P 62,414 3,091,442 5/1963 Romig 61 a] 263/32 Flled 3,091,443 5/1963 Hfil'Z et al. 263/32 F Dec-14,197 3,366,374 l/l968 Bay et al. 263/32 Asslgnee California Portland Cement Company 3 437 325 4/1969 Putnam et an 263/32 Los g Cam.

Primary Examiner-John .l. Camby Attorney-White, Haefliger and Bachand ROTARY KlLN CONTROL APPARATUS AND PROGRAMMHNG 119 Cl i 9 D i Fi ABSTRACT: Rotary kiln operation'is controlled so as to result in satisfactory kiln performance and high quality clinker US. Cl. 263/32, produmion Over long pen-eds chime. Main burner fuel supply 236/ B is controlled when the maximum temperature of materials in F27) 7/20 the kiln is in one range, and kiln speed of rotation is controlled lFlelld of Search 22633661125 when Such maximum temperature is in another range Also and the cooler speed of movement is controlled in relation to kiln speed of rotation and raw mix feeder speed.

r0 ram P0732 T0 COM/U TEN? ZOO air is passed to the kiln via a clinker cooler, for preheating,

PATENTEUUELMIBYI 3627,28?

sum 2 BF 5 Y .Z 8 DECREAS? 4 3 L 2 I 2 I X KS a, DECREASE G 5 I w KS CONSTANT 1 -hum ac a co/vsr-AA/r .Z'NVEA 70/2 (Essa/H. H52 2:

FUEL.

0 Remover/01v 10o PATENTEU on: I 4 15m SHEET 0F 5 5/1/75? FROM ELOCK 9, FIG. 3-

ECE O0 YES STOKE 7215 IN 'ivu" $7025 7'54! 14/ "MM so; VE BASE EQUATION N04 /2 All/D STORE IQESt/Z. 7' IN TIME COUNTER VALUE IN TIME COUNTER sou/5 845E EQUATION N0. 8 AN!) 570185 /N l 4N0 OUTPUT SECTION 60 THROUGH PILOT LOG/C AND SOLV F0? P,

(super 0,

TIME cow/r59 3 (ts) mo P i rss SOLVE 545E f'Ol/Af/O/V N0. 10 4ND 57095 IYESULT /S VAL UE l/V YES (ts) m0 fir rams/EM:

BACKGROUND OF THE INVENTION This invention relates generally to improvements in the control of kiln treatment of calcareous materials; and more specifically concerns rotary kiln control apparatus and programming.

The stability of operation of a rotary kiln to produce Portland Cement clinker is affected by many factors. Should these factors not be properly related and adjusted with time, kiln operation will become unstable, poor quality clinker will be produced, and control of the kiln may be lost, leading to excessive downtime and serious loss of economy.

SUMMARY OF THE INVENTION It is a major object of the invention to provide apparatus and method, including computer programming, for controlling kiln operation in such manner as to result in satisfactory kiln performance and high quality clinker production over long periods of time, problems of instability being thereby obviated. This objective is basically realized in accordance with the invention through control of main burner fuel supply when the maximum temperature of the materials in the kiln is within one range, and through control of kiln speed of rotation when the maximum temperature of such materials is within another range, as will be seen. In addition, close control of the kiln during startup is aided through relating the materials feeder speed increase to kiln speed increase in a manner to be described; control of the speed of a traveling grate cooler is effected by programming for stabilizing secondary air preheating; and pilot fuel flow as well as main damper valve positioning is closely controlled in relation to other parameters, for optimizing kiln operation.

Regarding process, the environment of the invention involves control of kiln speed and main burner fuel supply to in turn control the heating and exothermic reaction of raw materials flowing in the kiln under normal operating conditions; excursions of the maximum or near maximum temperature of the materials in the kiln are sensed; the main burner fuel supply is increased as the sensed temperature decreases within one range while the kiln speed is maintained substantially constant; and the kiln speed is decreased as the sensed temperature decreases within another predetermined range while the main burner fuel supply rate is held substantially constant. As will be seen, the method also involves the step of relatively rapidly increasing the kiln speed as the sensed temperature increases within a third range overlapping the said other range and after the kiln speed has been reduced to a predetermined low level, while maintaining the main burner fuel supply substantially constant.

It is another object of the invention to perform the above changes in kiln speed and main burner fuel supply as predeter mined linear functions of changes in the value of a parameter AT, which corresponds to the difference between a predetermined desired maximum temperature of the materials in the kiln and the sensed maximum temperature of those materials in the kiln.

It is another object of the invention to provide means for determining actual values of fuel supply rate and kiln speed as related to AT, values, as well as means for determining actual values of feeder speed in relation to kiln speed during startup; main damper valve position; pilot burner fuel flow rate, and cooler grate speed, as will be seen.

These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following description and drawings, in which:

DRAWING DESCRIPTION FIG. 1 is a vertical section through a kiln system controllable in accordance with the invention;

FIG. 2 is a graph illustrating control principles;

FIG. 3 illustrates a program outline for computer control of the FIG. I kiln;

FIG. 1 illustrates a program outline for computer control of FIG. ll kiln startup;

FIG. 5 illustrates a program outline for computer control of the traveling grate seen in FIG. ll;

FIG. 6 is a graph;

FIG. 7 is a graph;

FIG. 3 is a graph; and

FIG. 9 is a control system diagram.

DETAILED DESCRIPTION Referring first to FIG. II, a rotary kiln is generally indicated at M) as having elongated tubular shape and as being inclined from the horizontal. Raw materials are fed at it into the upstream open end R2 of the kiln which projects into a housing I3. The raw materials, which typically contain SiO A1 0 Fe 0 CaCo MgCo Na O and R 0 in correct proportions to produce Portland Cement, travel lengthwise downstream through the kiln, principally in response to rotation thereof, which may be effected by any suitable means such as is generally indicated at M. Furthermore, the kiln rotary speed may be controlled as desired, and in the past it has been generally the practice to attempt to control materials flow within the kiln by changing the speed of kiln rotation.

After passing downstream through the kiln, the materials discharge as clinker shown dropping at ll5 within hood llti into which the open downstream end 117 of the kiln projects. The clinker falls downwardly upon a grate means I8, where the clinker is retained in heat transfer relation with intake airstreams moving upwardly as indicated at 19 and 2t) and through the clinker bed 21. It will be understood that the clinker bed slowly travels along the length of the grate l3, which may be moved as by means of the drive generally shown at 22. The grate I3 and clinker bed Eli are confined within a clinker cooler housing 23 having an entrance at 2A for air delivered through duct 25, a stack 26 remote from the hood l6, and a clinker discharge outlet 27. Merely for purposes of illustration, the grate I8 is shown as supported on pivoted links 28 accommodating arcuate movement of the grate in response to operation of the drive means 22. The latter may include a motor 259 having a shaft 30, a coupling 31, another shaft 32 for driving the crank 33, and a link 3 connected between the crank and the grate. Also, the air duct 25 is shown as supplied with air by a suitable blower 35 through a damper 36.

In operation, air delivered through the duct 25 passes upwardly through the clinker bed 211 for the purpose of preheating the air and cooling the clinker, following which the air flows upwardly through the hood I6 and into the downstream end of the kiln. Fuel is delivered to the: downstream end of the kiln through a nozzle 37, the fuel becoming ignited for combustion with the air oxygen at a point 33. The fuel which may comprise natural gas, oil, powdered coal, or any suitable flowable combustible, is typically supplied to the nozzle 37 through a conduit 39. If natural gas is used, it may be supplied through an auxiliary line A l) into which a valve All and orifice meter A2 are connected. If oil or powdered coke or coal are used, they may be supplied to line 39 through suitable inlets, and primary air may be delivered to the conduit 39 through a line 43 into which a valve M is connected, a suitable blower 45 being shown for delivery primary air at desired pressure and volume to the conduit 39.

Means for secondarily preheating the intake air, which may take different forms, is shown in one of its forms at 50 in the throat region of the clinker cooler so as to be directly in the path of the preheated airstream flowing to the downstream end of the kiln. While the heater may take different forms, it is shown in FIG. ll merely for purposes of illustration as a gas burner to which gas is supplied through a line 511 in which an orifice meter 52 is connected for metering measurement purposes. As shown, line 51 may be supplied by either of lines 53 and 54, line 53 delivering a side stream of gas from the main conduit 39 and through a control valve 55, and line 54 delivering an independent side stream of gas through a control valve 56, the latter being preferred.

The purpose of the heater 50 is to controllably and additionally heat the incoming or secondary air prior to combustion of the main fuel stream in the kiln, thereby to control or adjust the combustion within the kiln to vary the regional location lengthwise of the kiln at which the hot gas reaches temperatures in excess of the materials maximum temperature. As a result, the temperature and the movement of the materials in the kiln may be controlled, and particularly that movement of materials associated with fluidization thereof in the critical zone generally shown at 57 in FIG. 1.

For purposes of achieving primary stabilization of the air preheat temperature, the movement of grate 18 may be varied in response topressure changes of secondary air, as for example as shown in FIG. 1. Thus, a pressure sensing device 58 may be located beneath the grate 18 and the pressure conditions may be viewed on a meter or instrument 59. Also, the speed of grate movement may be controlled by a magnetic clutch 31 in the drive 22, or an equivalent device, the energization of the clutch being controlled electrically as by the rheostat 60. Accordingly, the drive 22 may be controlled to decrease or increase the speed of grate movement in response to a decrease or increase respectively in the secondary air pressure, as measured before the air passes through the clinker received on the grate. In this connection, it will be understood that a stable preheat temperature of the air passing through the clinker bed is associated with a stable thickness. If for any reason there should occur an increased discharge of clinker from the kiln, this change will result in a changed pressure as measured by the device 58 so that the grate drive may be adjusted in such manner as to adjust the bed thickness to reestablish the desired pressure, to which the desired stabilized preheat temperatures are related.

It will be understood that local changes in the downstream movement of materials in the kiln in response to fluidization within the critical zone shown at 57 in FIG. I, tend to disturb the heat transfer conditions within the kiln in such manner as to amplify the tendency for materials to so move. For example, an observed increase in the rate of movement of materials through the fluidization zone and toward the downstream end of the kiln results in the lowering of the total heat level in the exothermic area 157, which thereby causes a later fuel ignition, i.e. a shifting of the ignition point 38 further from the downstream end 17 of the kiln. This in turn results in the physical lengthening of the tip of the flame 62, and the heat level in the fluidization zone 57 of the kiln is increased, which tends to produce a further increase in the rate of flow of materials from and through the fluidization zone. If these chain reactions are not suitably dealt with, there results what is commonly known as the loss of the kiln."

Referring back to FIG. 1, it will be observed that the kiln speed is controllable as by means of a drive Ma receiving control input KS from computer 100; and the fuel flow rate to the main burner 37 is controllable as by means of an actuator 41a for the valve 41, the actuator receiving control input B from the computer 100. Also, the speed of a feeder 11a for materials being fed to the kiln at 11 is controllable as by means of a drive 101 receiving control input FK from the computer; the fuel flow rate to the pilot burner 50 is controllable as by means of an actuator 56a for the valve 56, that actuator receiving control input P, from the computer; the speed of the cooler grate 18 is controllable by the drive 22 the rheostat of which is controlled by an actuator 103 receiving control input CS from the computer; and the rate of flow of kiln gas to the stack at 104 is controlled by a main damper valve 105 variably positioned by an actuator 105a receiving control input MDV from the computer. Normally, the setting of valve 36 passing air to the underside of grate 18 is held constant.

In accordance with an important aspect of the process, the main burner fuel B and the kiln speed KS are controlled in response to changes in the sensed maximum, or .near maximum, temperature of the materials in the kiln so as to aid in maintaining equilibrium or stable conditions in the kiln, thereby preventing loss" of the kiln. As broadly considered, and assuming normal operation after startup, the main burner fuel flow rate is increased as the sensed maximum temperature of the materials in the kiln decreases within one predeter' mined range (a relatively high temperature range) while maintaining the kiln speed constant; and the kiln speed is decreased as the sensed near maximum temperature of the materials decreases within another predetermined temperature range (a relatively low temperature range), while maintaining the main burner fuel flow rate is maintained substantially constant.

More specifically, such temperature sensing apparatus may include a temperature sensing device 64, as for example a pyrometer, or Rayotube, or light. pipe directed to receive rays 65 emanating from area 157 at or near the maximum solids temperature T The variable signal from the sensor 64 is conducted by line 67 to a device 68 also having a constant signal input at 69 representing a predetermined desired maximum materials temperature T' The output of the device 68 represents the difference between the two inputs, or AT which is indicated on a suitable meter 66. Thus, the device 68 functions to compare or algebraically add the two inputs, and it may take many different physical forms, depending on the mechanical, hydraulic, pneumatic, electrical, or optical nature of the inputs and output desired. For example, in the case of electrical inputs, the device may comprise a Wheatstone bridge or a potentiometer; and in the case of pneumatic or gas pressure inputs varying with temperature, the device 68 may comprise a pair of Bourdon gauges, one for each input, and interconnected in opposition. Note also that the oxygen content of the kiln exhaust gas is monitored at 400, and a corresponding signal developed at 401 is returned to the computer.

Referring to FIG. 2, a highly effective method for controlling B and KS as outlined above is depicted in graphical form. The graph abscissa has the dimension AT,, which is the same as AT referred to above, and the ordinate has the dimension At, representing the negative of the temperature correction desired to restore the materials maximum temperature to the desired point represented by the intersection of the ordinate and abscissa lines.

As shown, the graphed function has seven segments labeled 1-7, respectively, corresponding to seven control equations as set forth below. This means that the correction value At, applicable at any time in the determination of B and KS will depend upon the value of AT, at that time. interpreting the graph segment 1, as the value AT, decreases along one predetermined range defined by the abcissas of that segment the value of B (below a selected maximum as determined by the value 41) is inversely adjusted, i.e. is increased, KS being held constant; as AT, decreases along segment 2, Ar, and B are held constant (i.e. the increase of B was arrested at a value considered normal for kiln operation prior to decrease of AT, to zero); as AT, falls below zero along short segment 3 the values KS and B are held constant; as AT, continues to drop along short segment 4, KS is reduced somewhat while B is held constant; and as AT, thereafter continues to drop within another predetermined range defined by the abcissas of line segment 5, the kiln speed KS is progressively slowed until a minimum kiln speed is reached. Thereafter, as the AT, increases along a third range defined by the abcissas of line segment 6 intersecting segment 5 at the lowest point of A2,, KS and At, are increased until KS reaches a maximum when Ar, equals zero. Finally, no change is made in KS, B or At, as AT, recovers toward zero along line segment 7.

The control equation defining the above line segments 1 and 2 applicable to control of B are as follows:

The control equations defining the above line segments 3-7 applicable to control of kiln speed KS are as follows:

R- 4) J-H U q- 4 A =(S (ATCH'UNQ Eq. 5

A -2 Alp m.) (2-20 [mt-w (SL7) X)] 6) Az.-=(SL7) (AT,)()

where SL,-SL, are slopes,

IN IN are intercepts,

w,x,y and Z are temperature differences relative to 7 as seen in FIG. 2, sgared in computer memory,

AT =AT =T T as referred to above (AT =the lowest value of AT, in FIG. 2, at the point where lines 5 and 6 intersect (A!,.) =the lowest value of At in MG. 2, at the point where lines 5 and 6 intersect.

Typical data for the control equations referred to in FIG. 2

is as follows:

Eq. No. Slope Intercept Net Equation l l AI,- AT 2 0 0 Ai 0 3 0 0 At, a 0 4 0 35F AI,- -35F 5 3 0 Ar, 3 AT 7 variable variable see FIG. 2 7 0 None A! 0 Actual values of parameters, including B and KS, used in kiln startup and control are calculated by the computer by solving the following base equations, and using values of Ar at any given time as determined by the appropriate control (or net) equations given above:

Certain symbols or parameters, some of which appear in the above equations are defined below, and also with reference to FIGS. 6, 7 and h.

R rate (ratio of feeder speed to kiln speed) at time t in percent of ultimate production rate m slope of a plot of 1'? versus time t (See FIG. 6)

z= elapsed time in hours since kiln feeder Ha was started R, percent of ultimate production rate initially admitted to kiln at time zero c exponential constant (See below) (FS) (FK) =feeder llla speed in r.p.m. at time t (I S) final feeder 11a speed in r.p.m. SM-ultimate production rate R intg. R (up 5 rate at time when lf is maximum (BP),- pilot burner fuel flow rate 0 =3 constant and is the minimum temperature differential (T -T at which the computer is allowed to exercise the limited degree of speed control (about I r.p.h.). One preferred value for c appears to be about F.

(tR) elapsed time in hours at which production rate R reaches [00 percent. This value not used by computer directly.

(FS), initial feeder speed in r.p.m. at time zero. This value not used by computer directly.

(KS), initial kiln speed in r.p.h. at time zero. This value not used by computer directly.

B actual fuel rate on main burner as transmitted back to the computer from the fuel flow controller (FS)' (FXY) actual feeder speed in r.p.m. as transmitted back to the computer (KS)' actual kiln speed in r.p.h. as transmitted back to the computer P pilot burner fuel to correct for the maximum solids temperature deviation.

K a constant in reciprocal F. (for solids temperature correction) T desired maximum solids temperature in F.

P =total pilot burner fuel M a constant which represents the r.p.h. decrease in kiln speed per F. of solids temperature deviation S the instantaneous value of kiln speed (KS) when the net change in solids temperature over the preceding 9 minute period has just changed from negative to positive T the instantaneous value of solids temperature (T' at the time at which S occurs.

(KS); startup kiln speed at time t during period while kiln speed is being increased up to its ultimate. (See FIG. 7) (KS),.- final ultimate kiln speed in r.p.h. (KS) without subscript is a general expression for killn speed in r.p.h. at any time t.

(ts) elapsed time in hours at which kiln speed reaches I00 percent of its ultimate B fuel on main burner at time 1 AB last change of B, as calculated B final required fuel on main burner at ultimate production Q a constant which is the Y-axis intercept of plot of IF uel lFlow Percent of Ultimate versus Production Rate Percent of Ultimate. (See FIG. 8)

t time value to be used in startup procedure P theoretical pilot burner fuel to correct the temperature of the cooler airflow K a constant in reciprocal F. (for cooler air correction) K a conversion constant which is the ratio of SClFkl at one line on main burner to SCFH at one line on pilot burner F =fraction of total combustion air originating in cooler T desired temperature (F.) of cooler air going to kiln T =rneasured temperature (1F.) of cooler air before pilot burner (KS) kiln speed (KS) kiln speed final T measured temperature of solid materials in the burning zone T desired temperature of solid materials in the burning zone Alpha a number representing maximum allowable burning zone temperature AT the difference between T and T' ATSM main fuel at present time At the negative of T MDV= main damper valve on kiln exhaust MLDV,r final position damper valve on kiln exhaust CS cooler speed CS, cooler speed final P= pilot fuel 0 oxygen content in kiln exhaust gases UGP= undergrate pressure of grate cooler K a constant to be determined by operations Sector a location within the computer program NN) =identification of such sectors Counter a location within the computer program to count time T=identification of such counter ts =a predetermined time to end the startup procedure" R rate (ratio) Q =theoretical fuels at zero production SL =slope IN =intercept X) a number representing the temperature Y) differential relative to T Z) "M v 7 used in the controlequations Erratic temperature behavior is very common in rotary cement kilns due to the somewhat.uncontrollable flow of the raw mix, as well as due to raw mix decomposition caused by size differential within the raw mix and variations of trace elements present in the raw mix. When theraw mix continuously enters the rotary kiln, in a premeasured quantity, its downward motion is propagated mainly due to the rotating motion of the rotary kiln, which is installed at a slope, until the raw mix reaches zone D" explained in U.S. Pat. No. 3,09 I ,442, that zone being located at 57 in FIG. 1 herein. The motion of the mix through zone 57 does not depend entirely on the rotating motion of the kiln, but it is a motion of a fluidized bed, somewhat like water. Due to the variation of flow within the rotary kiln, the quantities reaching zone 57 can vary which in turn will affect the temperature in zone 157 (see U.S. Pat. No. 3,091,442). Such temperature changes then will be corrected by the computer control logic performing the calculations indicated in equations 8-15 above.

Typical logic or program steps characteristic of computer operation to control the kiln during normal operation after startup are shown in FIG. 3. Thus, the output pulses to control the settings for (KS),-, (FK (B (P (MDV); and (C are indicated in step 27 as updated at regular intervals, as for example every three minutes.

Block 28 indicates that the settings of the control devices 41a, 101, 14a, 13, 56a and 1050 are monitored for return to the computer. A block diagram showing one servocontrol scheme is shown in FIG. 9. Digital signals, as for controlling the main burner fuel valve actuator 41a, are generated by the computer, in accordance with equation 11 and step 27 in FIG. 3. Those signals are converted at 150 to the analog signal 151 fed to the comparator 152. The latter also receives an analog signal 153 generated by the position transducer 154, such as a rotary potentiometer or encoder. As actuator 41a drives the valve 41, the transducer 154 is also driven at 155.,Any difference between the signals 151 and 153 is detected by the comparator 152 to produce an output error signal 6 transmitted via operational amplifier 156 and power amplifier 157 to drive the servomotor 158 (coupled to actuator 41a until the error is eliminated, at which time the valve has been brought to calculated position. The error signal 6 may be returned to the computer at 159 to actuate the alarm seen in box 30 in FIG. 3, ife does not go to zero.

FIG. 4 illustrates a startup sequence which is enabled from blocks 9 and 10 in FIG. 3. In such startup, the kiln is brought up to final speed, automatically, in accordance with FIG. 7; the materials feeder is brought up to final speed (FS),.- more slowly in accordance with FIG. 7, and the ratio R of kiln speed to feeder speed increases in accordance with FIG. 6. Also, the main fuel B is increased as in FIG. 8. These relationships permit close control of the kiln by the computer in bringing the kiln under control pursuant to FIG. 2, using Ar for correction.

When the kiln speed reaches a predetermined percentage (30 percent in FIG. 4, for example) of its final speed, the startup calculations of FIG. 4 are performed, and the results are used immediately in block 27 of FIG. 3 to commence control of the kiln parameters. Thereafter, the program of FIG. 6

takes over as the kiln comes up to speed, the equation 10 value for (KS controlling the speed increase as 1 increases to increase the value of R in equation 10. Once the t-counter count reaches percent of a given startup time, the control is returned to block 11 and subsequent blocks, in FIG. 3.

The blocks in FIGS. 3-5 may be considered as means (as for example specific connections in the computer) to perform the functions identified therein.

More specifically, and in FIG. 3, initiation of the ECR (executive control routine) results first in testing whether the kiln is operating (block 1). If it is, a continual time test is made, and at 3 minute intervals (block 3) the inputs to the computer, as seen in the upper left hand corner of FIG. 1 are scanned (block 3a). In addition, a sample of the raw mix being fed to the kiln is X-rayed and the results in terms of percentage composition are scanned for use in raw-mix control as described in John R. Romig application for U.S. Pat., Ser. No. 18,517.

At hourly intervals (block 3), additional scanning is effected (block 3a). Blocks 4, 5 and 6 represent reading and storing, in memory, of certain variables as indicated. Blocks 7 and 8 represent testing for kiln temperature and alarming" if that temperature is excessive. The box 9 command effects initiation of the startup calculations of FIG. 4, as indicated in box 10 of FIG. 3.

In FIG. 4, assuming startup, block 200 represents a test to determine if the kiln speed KS has reached a predetermined percentage (30 percent, for example) of final speed (up to that speed, kiln speed control can be manually influenced). If it has not, the program starting with block 1 is resumed; but, if it has, inputs T and T are read and stored in memory sectors as indicated in block 201. Blocks 202-206 represent calculations and storage of results, the 203 step being performed at intervals (say 3 minutes, for example).

Block 207 tests for the existence of a time-counter value equal to or greater than that at (1.0 as shown in FIG. 7. If no, the calculation of 208 and 210 are performed and reinserted in the program as shown, and the program of FIG. 3 is reentered at block 27, as per block 213 in FIG. 4. If yes," the value of (KS) is stored as per block 209, and the calculations of block 210 carried out, followed by time testing at block 211 and reentry of the FIG. 3 program at block 11, as per block 214 in FIG. 4. Block 212 negates the command startup because full production speed of the kiln (KS) F was reached at (ts), as tested in block 211.

Referring back to FIG. 3, blocks 11-21 represent calculations, with block 19 referring to equations l-7. Block 22 represents an adjustable top limit of P to be used (if calculated P is too great) so as not to consume too much oxygen at the pilot burner zone. Block 23 and 24 represent the control of MDV setting as a function of the exhaust gas oxygen monitored at 400, the purpose being to so control that MDV setting as to keep exhaust gas oxygen below I percent, for process efficiency (i.e., the more 0 in the exhaust, the more heat is wasted in heating by unused air).

Block 25 represents a command setting which is enabled when full production is reached, Le, at tirne ttflb or thereafter, in FIG. 7, both kiln speed and feeder speed having reached maximum. Blocks 27 and 28 represent computer control of the various actuators as referred to in FIG. 1, based on calculated values therefor. The program is repeated, as indicated in block 403 in FIG. 3, and the startup calculations of block 10 and FIG. 4 are omitted during normal running.

FIG. 5 illustrates a control sequence for the traveling grate cooler 18 seen in FIG. 1. as further identified by box 26 in FIG. 3. Upon command input to the computer, as seen in block 25 in FIG. 3, the cooler control routine is performed. The cooler equations referred to in FIG. 3 to be solved are as follows:

exists in relation to kiln speed. This is of importance for the recuperation of available heat. The three values associated with blocks 13, M and 115 in FIG. 5 are used for grate speed control in such manner as to achieve temperature stabilization of air fed to the kiln via the grate. The values in blocks 13 and 14 represent the upper and lower limits of the grate speed outside of which the grate speed is to be increased or decreased Whereas the value in block 15 represents a grate speed between those limits for which the grate speed need not be changed. Thus, if the secondary air pressure decreases, the grate speed is reduced, to allow an increase in the clinker bed thickness on the grate so as to in turn produce an increase in secondary air pressure, and vice versa.

lclaim:

l. In a cement kiln control system wherein the kiln speed of rotation and the main burner fuel supply rate are controlled to in turn control the heating and exothermic reaction of raw materials flowing in the kiln, the process that includes:

a. sensing excursion of the near maximum temperature of materials in the kiln,

b. increasing the main burner fuel as said sensed near maximum temperature decreases within one predetermined range, while maintaining the kiln speed constant, and

c. decreasing the kiln speed as said sensed near maximum temperature decreases within another predetermined range, while maintaining said main burner fuel supply rate substantially constant.

The Pro s ts iml. ns mathssQaQ iB Em the kiln speed as said sensed nea aximum temperature increases with a third temperature range overlapping said other range, and after the kiln speed has been reduced to a predetermined low level, while maintaining said main burner fuel supply rate substantially constant, the rate of said kiln speed increase as a function of said sensed temperature increase exceeding the rate of said kiln speed decrease as a function of said sensed temperature decrease.

3. In a cement kiln control system wherein the kiln speed of rotation and the main burner fuel are controlled to in turn control the heating and exothermic reaction of raw materials flowing in the kiln, the process that includes:

a. deriving digital values representative of kiln rotary speed KS and main burner fuel rate B,

b. deriving a value AT, which corresponds to the difference between a predetermined desired maximum temperature of the materials in the kiln and the sensed maximum temperature of the materials in the kiln,

c. adjusting the value of B, below a selected maximum, in-

versely with the value of AT, when the value is within one predetermined range, and adjusting the value of KS directly with the value of A, when that value is within another predetermined range, and

d. using the adjusted values B and MS to control the main burner fuel flow rate and the kiln rotary speed, respectively.

4. The process of claim 3 wherein the value of B is adjusted as described when AT, is positive, and the value of KS is adjusted as described when AT, is negative, AT, being obtained by subtracting the predetermined desired maximum temperature of the materials in the kiln from the sensed maximum temperature of the materials in the kiln.

5. The process of claim 3 wherein the value of B is held at the selected maximum while the value of MS is adjusted as described.

6. The process of claim 3 wherein the value of 1K8 is held at a selected maximum while the value of B is adjusted as described.

'7. The process of claim 3 wherein the adjustment of the value of 1B is effected by obtaining a value At, which varies linearly with AT, in said one range, and using Al, to reduce B as AT, increases in that range.

it. The process of claim 3 wherein the adjustment of the value of KS is effected by obtaining a value At, which varies linearly with AT, as AT, increases in said other range, and using Al, to reduce KS as AT, increases in that other range toward a maximum.

9. The process of claim h wherein the adjustment of the value of KS is effected by obtaining a value At, which varies linearly with AT, and AT, decreases in said other range, and using Al, to increase KS as AT, decreases in said other range from said maximum.

llfl. The process of claim 3 wherein the digital value its is substantially as follows:

l ls E R h [moors 0 "1 where R= [0.05 mt +R llc m a selected constant 1 elapsed time R, =percent of ultimate production rate initially in kiln (lsh the startup interval time c a selected constant (KS) =final kiln speed, i.e. during normal operation 1111. The process of claim 3 wherein the digital value B is substantially equal to the value therefor in equation ill of the above specification.

12. The process of claim 3 wherein the pilot fuel is combusted to preheat air flowing to the kiln, the value 1P for pilot burner fuel flow being substantially equal to the value therefor as set forth in equations 13, 114 and 15 of the above specification.

13. The process of claim 3 wherein raw materials are fed to the kiln at a feeder speed rate FS, and wherein during startup of the kiln the kiln speed is increased at a rate greater than the rate at which FS is increased.

M. The process of claim 13 wherein during normal operation of the kiln the materials feed rate to the kiln is maintained in fixed relation to the kiln speed.

15. The process of claim ll wherein a traveling grate cooler receives clinker discharging from the kiln and air flowing to the kiln passes through clinker on the grate for preheating, and including the steps of calculating, limits associated with under grate air pressure and outside which the grate speed is to be increased or decreased, and controlling the grate speed in accordance with changes in under grate air pressures outside those limits.

lltS. ln a cement kiln control system wherein the kiln speed of rotation and the main burner fuel supply rate are controllable to in turn control heating and exothermic reaction of raw materials flowing in the kiln, the combination comprising,

a. first means for sensing excursions of the near maximum temperature of materials in the kiln,

b. second means for increasing the main burner fuel as said sensed near maximum temperature decreases within one predetermined range, and

c. third means for decreasing the kiln speed as said sensed near maximum temperature decreases within another predetermined range,

d. said second and third means including a computer.

117. In the control of a cement kiln system that includes a rotary kiln, a raw mix feeder, and a movable clinker cooler, the startup steps that include,

a. increasing the kiln speed of rotation to a predetermined value,

b. thereafter increasing the kiln speed of rotation to a final value while increasing the speed of the raw mix feeder to deliver raw mix to the rotating kiln for heating and exothermic reaction therein productive of clinker discharging from the kiln onto a clinker cooler,

c. passing air to the kiln via the clinker on the cooler, for combusting primary fuel to heat the raw mix in the kiln, and

the kiln to maintain said oxygen content below a predetermined level.

19. The method of claim 17 wherein the raw mix feeder speed increase in controlled in predetermined relation to the increase of kiln speed of rotation.

UNITED STATES. PATENT OFFICE v CERTIFICATE OF CORRECTION Patent 3$271,287 Dated December 14, 1971 Inventor(s) Joseph H. Herz It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4; delete the entirety of line 71, and substitute At (SL QT (IN Eq. 1

Column 4; delete the entirety of line 72, and substitute --At (SL HAT (1N Eq. 2

Column 5, line 12; "w,x,y" should read W, X, Y

Column 10; delete the entirety of line 17, and substitute Column 11, lines 2 and 3; "speed of rotation and the speed of the raw mix feeder having increased to final values." should read speed of rotation and the speed of the raw mix feeder have increased to final values.

Signed and sealed this L th day of July 1972.

(SEAL) Attest:

EDWARD I RFLETCHER, JR. I ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM po'mso USCOMM-DC eoavs'pos a [1.5. GOVERNMENT PRINTING QFFIC I 9"9 O 3i6"33 

1. In a cement kiln control system wherein the kiln speed of rotation and the main burner fuel supply rate are controlled to in turn control the heating and exothermic reaction of raw materials flowing in the kiln, the process that includes: a. sensing excursion of the near maximum temperature of materials in the kiln, b. increAsing the main burner fuel as said sensed near maximum temperature decreases within one predetermined range, while maintaining the kiln speed constant, and c. decreasing the kiln speed as said sensed near maximum temperature decreases within another predetermined range, while maintaining said main burner fuel supply rate substantially constant.
 2. The process of claim 1 including the step of increasing the kiln speed as said sensed near maximum temperature increases within a third temperature range overlapping said other range, and after the kiln speed has been reduced to a predetermined low level, while maintaining said main burner fuel supply rate substantially constant, the rate of said kiln speed increase as a function of said sensed temperature increase exceeding the rate of said kiln speed decrease as a function of said sensed temperature decrease.
 3. In a cement kiln control system wherein the kiln speed of rotation and the main burner fuel are controlled to in turn control the heating and exothermic reaction of raw materials flowing in the kiln, the process that includes: a. deriving digital values representative of kiln rotary speed KS and main burner fuel rate B, b. deriving a value Delta Tc which corresponds to the difference between a predetermined desired maximum temperature of the materials in the kiln and the sensed maximum temperature of the materials in the kiln, c. adjusting the value of B, below a selected maximum, inversely with the value of Delta Tc when the value is within one predetermined range, and adjusting the value of KS directly with the value of Delta Tc when that value is within another predetermined range, and d. using the adjusted values B and KS to control the main burner fuel flow rate and the kiln rotary speed, respectively.
 4. The process of claim 3 wherein the value of B is adjusted as described when Delta Tc is positive, and the value of KS is adjusted as described when Delta Tc is negative, Delta Tc being obtained by subtracting the predetermined desired maximum temperature of the materials in the kiln from the sensed maximum temperature of the materials in the kiln.
 5. The process of claim 3 wherein the value of B is held at the selected maximum while the value of KS is adjusted as described.
 6. The process of claim 3 wherein the value of KS is held at a selected maximum while the value of B is adjusted as described.
 7. The process of claim 3 wherein the adjustment of the value of B is effected by obtaining a value tc which varies linearly with Delta Tc in said one range, and using tc to reduce B as Delta Tc increases in that range.
 8. The process of claim 3 wherein the adjustment of the value of KS is effected by obtaining a value tc which varies linearly with Delta Tc as Delta Tc increases in said other range, and using tc to reduce KS as Delta Tc increases in that other range toward a maximum.
 9. The process of claim 8 wherein the adjustment of the value of KS is effected by obtaining a value tc which varies linearly with Delta Tc as Delta Tc decreases in said other range, and using tc to increase KS as Delta Tc decreases in said other range from said maximum.
 10. The process of claim 3 wherein the digital value KS is substantially as follows: (KS)S Congruent R (KS)F Divided by (m(ts)100 + Ro c)1/c where R (0.05 mt + Roc1/c m a selected constant t elapsed time Ro percent of ultimate production rate initially in kiln (ts)100 the startup interval time c a selected constant (KS)F final kiln speed, i.e. during normal operation
 11. The process of claim 3 wherein the digital value B is substantially equal to the value therefor in equation 11 of the above specification.
 12. The process of claim 3 wherein the pilot fuel is combusted to preheat air flowing to the kiln, the value PT for pilot burner fuel flow being substantially equal to the value therefor as set forth in equations 13, 14 and 15 of the above specification.
 13. The process of claim 3 wherein raw materials are fed to the kiln at a feeder speed rate FS, and wherein during startup of the kiln the kiln speed is increased at a rate greater than the rate at which FS is increased.
 14. The process of claim 13 wherein during normal operation of the kiln the materials feed rate to the kiln is maintained in fixed relation to the kiln speed.
 15. The process of claim 1 wherein a traveling grate cooler receives clinker discharging from the kiln and air flowing to the kiln passes through clinker on the grate for preheating, and including the steps of calculating limits associated with under grate air pressure and outside which the grate speed is to be increased or decreased, and controlling the grate speed in accordance with changes in under grate air pressures outside those limits.
 16. In a cement kiln control system wherein the kiln speed of rotation and the main burner fuel supply rate are controllable to in turn control heating and exothermic reaction of raw materials flowing in the kiln, the combination comprising, a. first means for sensing excursions of the near maximum temperature of materials in the kiln, b. second means for increasing the main burner fuel as said sensed near maximum temperature decreases within one predetermined range, and c. third means for decreasing the kiln speed as said sensed near maximum temperature decreases within another predetermined range, d. said second and third means including a computer.
 17. In the control of a cement kiln system that includes a rotary kiln, a raw mix feeder, and a movable clinker cooler, the startup steps that include, a. increasing the kiln speed of rotation to a predetermined value, b. thereafter increasing the kiln speed of rotation to a final value while increasing the speed of the raw mix feeder to deliver raw mix to the rotating kiln for heating and exothermic reaction therein productive of clinker discharging from the kiln onto a clinker cooler, c. passing air to the kiln via the clinker on the cooler, for combusting primary fuel to heat the raw mix in the kiln, and d. increasing the cooler speed of movement after the kiln speed of rotation and the speed of the raw mix feeder have increased to final values.
 18. The method of claim 17 including monitoring the oxygen content of the kiln exhaust gas produced by said combustion, and controlling the rate of escape of exhaust gas from the kiln to maintain said oxygen content below a predetermined level.
 19. The method of claim 17 wherein the raw mix feeder speed increase is controlled in predetermined relation to the increase of kiln speed of rotation. 